Hi

I noticed with my X300, that with a high way speed (abt. 130 km/h) the car starts shaking/vibrating. The tyres are recently balanced, so that’s not the issue. One think I doubt a bit is the tyre pressures, as according to the manual they should be at level 1,8-2,0 bar but my tyre dealer who made the balancing insisted to put minimum 2,5 bar. He said that the tyres have totally different structure than earlier and any lower pressure would damage the tyres. After the vibration experience, I anyhow lowered the pressures, but no big effect to the vibration even it felt generally a bit more comfortable.

Now I am a bit skeptic about the model/make of the tires, as they are a kind of “budget” brand. They were just installed to the car when I bought it and thus almost brand new.

Any experiences?

 

Bad tyres (and warped wheels) can cause vibration, but I'd expect it to become apparent at much lower speeds.

I would look at Propshaft centre bearing, Jurid coupling at the Diff end of the propshaft, rear half shaft universal joints. Plus the propshaft alignment if anything has been disturbed recently.

 

Switch tires front to rear. Any difference? If so, it suggests a wheel or tire problem.

Generally, a wheel tire problem in front will make the steering wheel shake. A wheel tire problem in the rear will be felt more in the body of the car. U-joint and prop shaft problems will more likely feel like a vibration coming up through the floor.

None of the above clues being carved in stone, though

Cheers
DD

 

I think it is unlikely that the higher tire pressure is a contributor to your vibration. On our '93 XJ40 (same chassis as the X300), I experimented with various tire pressures within the recommended ranges and settled on 33 psi (2,275 bar) for the front tires and 36 psi (2,5 bar) for the rears. This gave what I considered to be the best combination of handling and ride.

One possibility is that the tires balanced well enough at lower speeds on the balancing machine, but that a slight imbalance or an imperfection in one or more tires is leading to vibration at higher speeds. In the U.S., some tire shops use Hunter Road Force balancing machines that simulate the weight of the vehicle while determining the required balancing weights and positions. If any shops in your area have a Hunter Road Force machine it might be worth having them check the balancing of your tires. I once bought a used BMW on which the dealer had installed cheap Nexen tires which vibrated at high speeds. Two tire shops could not improve the balance, but a third shop with a Hunter Road Force machine completely solved the imbalance:


I like Doug's idea of rotating the tires front-to-rear to see if the symptoms change.

Cheers,

Don